1. Field of the Invention :
This invention relates to an optically active pyrimidine compound which is a liquid crystal compound useful as an electrooptic element wherein the response of the ferroelectric smectic liquid crystal to an electric field is utilized.
2. Description of the Prior Art :
Liquid crystals have been employed as various electrooptic elements such as a display device of a watch or an electronic calculator. Most of liquid crystal display devices which have been put into practical use hitherto are those wherein the dielectric orientation effect of a nematic or cholesteric liquid crystal is utilized. However the application of these liquid crystals to a display device involving a large number of pixels is accompanied by some troubles such as a low response, poor contrast caused by the lack of drive margin and unsatisfactory visual angles. Therefore there has been frequently attempted to develop a MOS or TFT panel involving formation of a switching device for each pixel.
U.S. Pat. No. 4,367,924 has disclosed a liquid crystal device wherein a smectic phase based on a novel displaying principle is used to thereby overcome the disadvantages as described above.
Further it has been known that a liquid crystal compound exhibiting a C* or H phase consisting of optically active molecules generally has an electrical dipole density P and is ferroelectric. Such a chiral smectic liquid crystal having electrical dipoles is more strongly affected by an electric field than dielectric anisotropic ones. As a result, the polarity of P is made parallel to the direction of the electric field. Thus the direction of the molecules can be controlled by reversing the direction of the applied electric field. Then the average change in the direction of the major axes of these molecules is detected with the use of two polarizing plates. Thus the liquid crystal can be used as an electrooptic element.
The effect of the spontaneous polarization of this electrooptic element, wherein the response of the smectic C* or H phase to an electric field is utilized, and the electric field exert an action 10.sup. 3 to 10 .sup. 4 times as high as those of dielectric anisotropic ones. Thus the former shows a high-speed response compared with a TN liquid crystal device. Further it is possible to impart thereto a memory function by appropriately controlling the orientation. Therefore it is expected to apply the same to a high-speed optical shutter or to a display of a large capacity.
There have been synthesized various chiral smectic liquid crystal compounds having a ferroelectricity and the properties thereof have been studied.
For example, an optically active 2-(4-alkoxyphenyl)-5-alkylpyrimidine compound has been proposed as a compound which is stable to water and shows a chiral smectic phase within a wide range of temperature in Japanese Patent Laid-Open No.93170/1986.
However each compound as described above is available only within a restricted range of temperature. Namely, its insufficient properties, in particular, at a low temperature make it unsatisfactory from the practical viewpoint.